In the past, in making a transportation type vehicle such as a bus, or a car for a mass transportation system, it has been customary to erect on a partly completed chassis or base structure the frame structure or shell for the sidewalls and roof of the vehicle, which is then completed by the installation of electrical wiring, air conditioning equipment, heating and cooling ducts, fixtures, trim, seats, floor covering, etc. Such "stick type" construction is slow and costly, with artisans of various trades working interiorly of the car from the time the sidewall and roof frames or shells are erected on the base structure until the final interior decoration is completed and the floor covering laid. Such work is difficult to plan, schedule, supervise, and perform, and there is a constant possibility that one or another crew of workers may damage or soil work already performed, thereby causing duplication and delay and adding to cost.